Cleaning of metal by electrolysis



Patented Sept. 7, 1926.

UNITED STATES IVAR H. LEE, 013 DETROIT, MICHIGAN, ASSIGNOR TO THE STUDEBAKER CORPORA- TION, OF SOUTH BEND, INDIANA.

1,598,731 PATENT OFFICE.

A CORPORATION" OF NEW JERSEY.

CLEANING OF METAL BY ELECTROLYSIS.

no Drawing.

This invention relates to a method of cleaning the surface of iron or steel articles, and particularly to that method wherein the articles to be cleaned are placed in an electrolyte and an electric current is passed therethrough.

Heretofore when such articles have been coatedwith dirt and grease and were, in addition, coated with n oxide of iron such as rust or scale, it has been the practice to subject them to a suitable alkaline bath which removes the dirt and grease, either alone or by the aid of an electric current, rcmove and rinse them, and then subject them to a second bath containing a mineral acid, often with the aid of an electric current, to remove the rust. Thus two distinct operations have been necessary to clean such articles, and in the second operation the acid in the bath has had a tendency to eat or pit the surface of the article. This eating or pitting will be particularly evident when a straight pickling operation is employed while in the use of an electric current the pitting action will be less evident, but still present. The cause in either case is the dissolving action of the acid on the metal, the dissolving of the metal beneath the oxide or rust loosening the latter so that it will fall or may be rubbed off. The use of an electric current causes cathodic hydrogen to be formed which partially protects the article being cleaned from the action of the acid as well as to loosen oxide or rust, but nevertheless the acid action on the metal still ref 'lllls. Furthermore, in cases where the metal of the article is somewhat porous, the acid often works its way into the pores and is not completely removed in the subsequent rinsing process, with the resultthat after the article has been put in service the acid works out to thesurface and causes the same to rust, and if the article has been covered with a coating of paint or enamel, it causes the latter to scale or loosen. The pitting of the surface of the article is highly detrimental in some classes of work, and it is the elimination of this pitting, and the simultaneous removal of grease and rust and other iron oxides as well as the prevention of subsequent rusting as described above that the present invention contemplates, as well as effecting saving in labor, time and material.

In accordance with the present invention I provide azrelectrolyte, composed of a solu- Application filed May 1, 1925. Serial No. 27,302.

tion of an organic acid, such as citric or tartaric acid, to which enough alkali, such as caustic soda or sodium carbonate, has been added to slightly more than neutralize it, or in other words, to make it slightly alkaline, The organic acid and the alkali join to form an alkali salt of an organic acid, which is neutral in reaction, and the electrolyte is in reality a water solution of such salt which has been made slightly alkaline by the addition of an exccss of the alkali. This solution is then preferably heated to about 180 Fahrenheit but preferably not less than 165 Fahrenheit and the iron or steel article to be cleanedv is hung on or clamped to a hook or other member connected to the negative side of lowtension direct electric current and immersed in the solution, the current passing thereto from an anodeof iron or other suitable material also immersed in the solution. lvVhile the removal of the grease and dirt and the rust, of course, occurs practically simultaneously, for the sake of explanation it is preferable to consider the action on each separately. In thus considering the action on the grease and dirt, the rapid evolution of the hydrogen at the oathode, Which the article forms, is instrumental in removing the same almost instantly, lifting it off so to speak, from the surface of the article. The grease being light ascends to the surface of the electrolyte where it is removed by the skimming or other process 'and the dirt usually is deposited on the bottom of the tank where it may be removed at convenient intervals.

In the removal of the oxides of iron on the surface of the article, whether it be the .ferric hydroxide commonly known as rust,

or ferric and ferrous oxides formed in thern'ro-meehanical operations, there are probably two actions that occur in the same, first, the ferric hydroxide and the other iron oxides may be gradually reduced to a lower form of iron oxide which may be soluble in the electrolyte, or which may be readily removed in the subsequent rinsing operation. or, second, it may be mecln'inically carried tl'irough the evolution of the hydrogen, or through a com bination of both.

Although any-organic acid may be used for the electrolyte, I prefer to use either citric. oxalic or tartarielacid. I have found that by using approximately four ounces of citric acid to one gallon of water, and

thereafter adding sufficient caustic soda to neutralize the acid, and then adding a small excess of caustic soda, say up to one ounce per gallon of solution to make it slightly alkaline, a very satisfactory electrolyte esults. The practical limits of the amount of resulting salt from the combination of the acid and the alkali per gallon of water is approximately from 6 to ltlounccs. lVith such a solution I prefer to use an electric currentof six to twelve volts and a current density of not less than 50 amperes per square footof surface of the articles being cleaned, the current density being varied according to the speed desired to' effect the cleaning. I have found that-with a current density of seventy-five amperes per square foot art cle surface a heavily rusted and very dirty and greasy article may be thoroughly cleaned in less than one-minute. After the article has been subjected to this cleaning process it is removed and rinsed and then preferably wiped to remove any particles of foreign matter that might be still clinging to its surface. Inasmuch asthis process uses a slightly alkaline electrolyte it will be evident that it has no action on the basic metal itself, and

consequently no pitting of the metal occurs.

Neither will the absorbing of any of the electrolyte by the pores of the metal have any subsequent effect on the metal. In addition, the double effect of removing the dirt and grease and the oxide is accomplished in one process in a much less space of time than heretofore used.

What I claim is 1. An electrolyte for use in the electrolytic cleaning offerrous articles, comprising a water solution of an alkali metal salt of an organic reducing acid which has been made slightly alkaline in reaction. 2. An electrolyte for use in electrolytic cleaning of ferrous articles at a temperature of not less than 165 Fahrenheit and a current density of not less than 50 amperes per square foot of article being cleaned, said electrolyte comprising a solution of an alkali metal salt of an organic reducing acid to which .1 to 4 ounces of an alkali has been added"pe r gallon of electrolyte.

3. An electrolyte for use in the electrolytic cleaning of ferrous articles at a temperature of not less than 18:33 Fahrenheit and a cur rent density of not less-than 5O amperes per square foot of surface" of article being, cleaned, comprising a solution of 6 to 16 ounces of an alkali salt of an organic reducing acid to which .1 to 4 ounces of an alkali has been added per gallon of electrolyte.

4;. The process of electrolytically cleaning ferrous articles which comprises subjecting said articles-to the action of a direct electric current of a density of not less than 50 am peres per square foot of surface being cleaned in an electrolyte of not less than 165 F ahrenheit. said electrolyte comprising a water solution of an alkali metal salt of an organic reducing acid which has been made slightly alkaline in reaction 5. The process of electrolytically cleaning ferrous articles which comprises subjecting said articles to the action of a direct electric current of not less than '50 amperes per square foot of surface to be cleaned in an electrolyte comprising asolution of 6 to 16 ounces of an alkali metal salt of an organic reducing acid per gallon of Water, said solution having been made slightly alkaline and being at a temperature of not less than 165 Fahrenheit.

6. An electrolyte for use in the electrolytic cleaning .of ferrous articles, comprising a citrate of an alkali metal which has been made slightly alkaline in reaction 7. An electrolyte for use in electrolytic cleaning of ferrous articles at a temperature of not less than 165 Fahrenheit and 2. current density of not less than 50 amperes per square foot of surface of articles being cleaned, said electrolyte comprising a solution of a citrate of an alkali metal to which .1 to t ounces of alkali per gallon of electrolyte has been added.

8 An electrolyte for use in electrolytic cleaning of ferrous articles at a temperature of not less than 165 Fahrenheit and a current. density of not less than 50 amperes per square foot of surface of article being cleaned, comprising a solution of 6 to 16 ounces -.of a citrate of an alkali metal and from .1 to 4 ounces of an alkali'per gallon of water.

' 9. The process of electrolytically cleaning ferrous articles which comprises subject-ing said articles to the actionof a direct electric current in an electrolyte at a temperature of not less than 165 Fahrenheit, said electrolyte comprising a solution of a citrate of an alkali metal which has been made slightly alkaline in reaction.

10. An electrolyte for use in the electrolytic cleaning of ferrous articles, comprising an oxalate of an alkali metal which has been made sli htly alkaline in reaction.

11. An electrolyte for use in electrolytic cleaning of ferrous articles at a tempera? ture of not less than 165 Fahrenheit and a current density of not less than 50 amperes per square foot of surface of articles being cleaned, said electrolyte comprising a solution of an oxalate of an alkali metal to which .1 to 4 ounces of alkali per gallon of electrolyte has been added.

12. An electrolyte for use in electrolytic cleaning of ferrous articles at a tempera-- ture of not less than 165 Fahrenheit and a current density of not less than 50 amperes per square foot of surface of article being cleaned, comprising a solution of 6 to 1.6 ounces of an oxalate of an alkali metal and from .1 to 4 ounces of an alkali per gallon of Water.

13. The process of electrolytically cleaning ferrous articles which" comprises'subjecting said articles to the action of a direct electric current in an electrolyte at a temperature of not less than 165 Fahrenheit, said electrolyte comprising a solution of an oxalate of an alkali metal which has been made slightly alkaline in reaction.

14. An electrolyte for use in the electrolytic cleaning of ferrous articles, comprising a tartrate of an alkali metal which has been made slightly alkaline in reaction.

15. An electrolyte for use in electrolytic cleaning of ferrous articles at a temperature of not less than 165 Fahrenheit and a current density of not less than 50 amperes per square foot of surface of articles being cleaned, said electrolyte comprising a solution "of a tartrate of an alkali metal to electrolyte has been added.

16. An electrolyte for use in electrolytic cleaning of ferrous articles at a temperature of not less than 165 Fahrenheit and a current density. of not less than 50 amperes per square foot of surface of article being 'rect electric current in an electrolyte at a temperature of not less than 165 Fahrenheit, said electrolyte comprising a solution of a tartrate of an alkali metal which has been made slightly alkaline in reaction.

Signed by me at Detroit, Michigan, U. S. A., this 28th day of April, 1925. I

IVAR H. LEE.

which .1 to 4 ounces of alkali per gallon of 

